What is Bietti’s crystalline dystrophy?
Bietti’s crystalline dystrophy (BCD) is a hereditary eye disease named after Dr G. B. Bietti, an Italian ophthalmologist, who labelled three patients with alike symptoms in 1937. This disease is also called Bietti’s crystalline chorioretinal dystrophy.
What causes Bietti’s crystalline dystrophy (BCD)?
Bietti’s crystalline dystrophy is produced by mutations in the CYP4V2 gene. This gene provides instructions for making a member of the cytochrome P450 family of enzymes. These enzymes are involved in the formation and breakdown of various molecules and chemicals within cells. The CYP4V2 enzyme is involved in a multi-step process called fatty acid oxidation in which lipids are wrecked down and converted into energy, but the enzyme’s specific function is not well understood.
CYP4V2 gene mutations that cause Bietti’s crystalline dystrophy damage or eliminate the function of this enzyme and are believed to affect lipid breakdown. Though, it is unknown how they lead to the exact signs and symptoms of Bietti’s crystalline dystrophy. For unknown reasons, the severity of the signs and symptoms differs significantly among individuals with the same CYP4V2 gene mutation. Bietti’s crystalline dystrophy patients and on the causes of the condition.
What are the symptoms of Bietti’s crystalline dystrophy (BCD)?
Symptoms of Bietti’s crystalline dystrophy comprise crystals in the cornea (the clear covering of the eye); bright yellow deposits on the retina; and broadminded atrophy of the retina, choriocapillaris, and choroids (the posterior layers of the eye). This tends to cause progressive night blindness and constriction of the visual field. BCD is a rare disease and appears to be more common in people of Asian descent.
People with BCD have crystals in some of their white blood cells (lymphocytes) that can be seen with an electron microscope. Researchers have not been able to determine exactly what substance forms these crystalline deposits. Its presence does not appear to harm the patient in any other way, except to affect vision.
Bietti’s crystalline dystrophy (BCD) treatment
There is no cure or treatment for Bietti’s crystalline dystrophy. Scientists hope to apply the findings of genetic research to develop an effective therapy.
Asians, especially those of Chinese ethnicity, have been found to have a relatively higher incidence of BCD.
Diagnosis of Bietti’s crystalline dystrophy (BCD)
The diagnosis of BCD is based on the ophthalmic evaluation of numerous small yellowish-white retinal crystalline deposits in the retina with or without crystalline deposits in the cornea, atrophy of the RPE, and sclerosis of the choroidal vessels. Corneal crystals are usually isolated in the anterior and subepithelial stroma of the peripheral cornea.
YP4V2 is only moderately expressed in the cornea and conjunctiva; therefore, ocular surface findings are not necessary for diagnosis. Diagnostic tools include electroretinography to assess the degree of rod and cone dysfunction, Humphrey visual field test for visual field deficits, spectral-domain OCT to identify reflective spots, in vivo confocal microscopy, and specular microscopy. If the clinical features are ambiguous, the disease can be confirmed by identifying pathologic variants in CYP4V2 using molecular genetic testing.
Typically, Bietti’s crystalline dystrophy patients begin to notice symptoms between the second and third decades of life. Patients experience a progressive discount in visual acuity, nyctalopia, and visual field loss. Colour vision can sometimes be exaggerated as well. Visual deficits can progress at different speeds in each eye, and the severity and speed of progression vary widely among affected people. Over time, patients, especially in their fifth or sixth decade, can become legally blind.
The differential diagnosis of Bietti’s crystalline dystrophy includes other diseases that involve crystalline deposits in the retina such as:
- Retinitis pigmentosa
- Type 1 and type 2 primary hyperoxaluria
- Infectious crystalline keratopathy
- Sjogren-Larsson syndrome
- Drug toxicity of agents such as tamoxifen, talc retinopathy, methoxyflurane, and canthaxanthin.